Power tool

ABSTRACT

A power tool ( 1; 90 ) includes a motor ( 17 ) having a stator ( 18 ) and a rotor ( 19 ). The stator ( 18 ) includes front and rear insulators ( 21, 22 ) respectively disposed forward and rearward of a stator core ( 20 ) in an axial direction thereof. At least six coils ( 23 ) are respectively wound on the stator ( 18 ) such that the coils ( 23 ) are wound through the front and rear insulators ( 21, 22 ). Winding wires ( 23   a ) respectively electrically connect circumferentially-adjacent pairs of the coils ( 23 ). A short circuiting device ( 25 ) short circuits respective pairs of windings ( 23   a ) that are located diagonally or diametrically across from one another.

CROSS-REFERENCE

The present application claims priority to Japanese patent applicationserial number 2013-188528 filed on Sep. 11, 2013, the contents of whichare incorporated fully herein.

TECHNICAL FIELD

The present invention relates to a power tool, such as a driver-drill,that comprises a motor serving as its drive source.

BACKGROUND ART

As disclosed, e.g., in US 2011/0043057 A1 (and its family member JP2011-45201 A), power tools equipped with a motor, such as a brushlessmotor, are well known. However, the overall structure of the electricmotor differs depending on the model (e.g., a light load model or aheavy load model) of the power tool.

For example, an electric motor for a light load model typically has astructure wherein the main current flows to a sensor circuit board via asolderable wire. On the other hand, in an electric motor for a heavyload model, lead wires (i.e., power supply wires) are typically directlyconnected to more robust fusing terminals (connecting terminals) due tothe higher current that flows therethrough.

SUMMARY OF THE INVENTION

Although electric motors for light (low) load power tools may have asmall size and thus be space saving, generally speaking such electricmotors are not capable of drawing (or being driven by) a large current,thereby limiting their applicability. In contrast, while electric motorsfor heavy (high) load power tools are designed to draw (or be driven by)a large current, such electric motors are generally larger than lightload electric motors and consequently are not suitable for making acompact power tool.

Accordingly, it is an object of the present teachings to disclose, forexample and without limitation, a compact power tool that utilizes arelatively small-sized motor capable of drawing a large current.

In a first aspect of the present teachings, a power tool preferablycomprises a motor that includes a stator and a rotor. A plurality ofcoils (e.g., at least six) are wound on the stator such that the coilsare wound through respective insulators located at the front and rear inan axial direction of the stator. The power tool further comprises ashort circuiting means that short circuits diagonally-positioned(diametrically-opposite) pairs of winding wires between the coils, ofwhich there are at least six.

In a second aspect of the present teachings, all of the coils arepreferably wound with one winding wire (a single continuous wire).

In addition or in the alternative to the second aspect, the shortcircuiting means preferably comprises: a plurality of sheet metalelements, which electrically interconnect the pairs of winding wiresbetween the coils (the winding wires that are diametrically opposite ofeach other), and an insulation part, which is made of resin and retainsthe sheet metal elements.

In addition or in the alternative to the first and/or the second aspect,the short circuiting means preferably is lead wires that electricallyinterconnect the pairs of winding wires between the coils.

In addition or in the alternative to any preceding aspect, a sensorcircuit board, which comprises a rotation detection device that detectspositions of permanent magnets provided on the rotor, is preferablyprovided between the insulator and the short circuiting means.

The sensor circuit board is preferably mountable at a different phase.

In another aspect of the present teachings, a power tool preferablycomprises a motor that includes a stator and a rotor. A plurality ofcoils are wound on the stator such that the coils are wound throughrespective insulators located at the front and rear in an axialdirection of the stator. A housing that houses the motor is formed bycombining a pair of half housings. The stator is provided with at leastone positioning part that engages with respective inner surfaces of thehalf housings.

In another aspect of the present teachings, a power tool preferablycomprises a motor that includes a stator and a rotor. A plurality ofcoils are wound on the stator such that the coils are wound throughrespective insulators located at the front and rear in an axialdirection of the stator. A housing that houses the motor is a tubularhousing. The stator is provided with at least one positioning part thatengages with an inner surface of the tubular housing.

Either of the above-noted positioning parts may be provided on theinsulator(s).

According to the present teachings, a compact power tool can be achievedby using a motor that can draw a large current, even though it is smallsized and space saving.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall view of a driver-drill according to the presentteachings.

FIG. 2 is a longitudinal cross sectional view of a main body rear partof the driver-drill.

FIG. 3 is a perspective, side view of a representative brushless motor.

FIG. 4 is a perspective, rear view of the brushless motor.

FIG. 5 is an exploded perspective view of the brushless motor.

FIG. 6 provides explanatory diagrams of a representative sensor circuitboard, wherein FIG. 6A is a front view thereof, and FIG. 6B is a crosssectional view taken along the B-B line in FIG. 6A.

FIG. 7 provides explanatory diagrams of the brushless motor, whereinFIG. 7A is a front view thereof, FIG. 7B is a side view thereof, andFIG. 7C is a rear view thereof.

FIG. 8A is a perspective, front view of a representative shortcircuiting element, and FIG. 8B is a perspective, rear view of the shortcircuiting element.

FIG. 9 provides explanatory diagrams of the short circuiting element,wherein FIG. 9A is a front view thereof, FIG. 9B is a side view thereof,and FIG. 9C is a rear view thereof.

FIG. 10 is an exploded perspective view of the short circuiting element.

FIG. 11 is an explanatory diagram that shows the arrangement of sheetmetal elements of the short circuiting element.

FIG. 12 shows a representative wiring diagram for the coils.

FIG. 13 is a cross sectional view taken along the A-A line in FIG. 2.

FIG. 14A is a perspective, front view of a representative tubularhousing, and FIG. 14B is a perspective, rear view of the tubularhousing.

FIG. 15A is a front view of the tubular housing, and FIG. 15B is a crosssectional view taken along the C-C line in FIG. 15A.

FIG. 16A is a cross sectional view taken along the D-D line in FIG. 15A,and FIG. 16B is a cross sectional view taken along the E-E line in FIG.15B.

FIG. 17 is a perspective view of another brushless motor, wherein theorientation of the sensor circuit board has been changed (rotated by180° as compared to the orientation shown in FIG. 3).

FIG. 18 is a longitudinal cross sectional view of a representativegrinder according to the present teachings.

FIG. 19 is a perspective view of a stator, wherein the attachmentposition of the sensor circuit board has been changed (as compared tothe attachment position shown in FIG. 3).

FIG. 20 shows explanatory diagrams of the stator in which the attachmentposition of the sensor circuit board has been changed, wherein FIG. 20Ais a rear view thereof, FIG. 20B is a side view thereof, and FIG. 20C isa front view thereof.

FIG. 21 is a cross sectional view taken along the F-F line in FIG. 20C.

FIG. 22 shows explanatory diagrams of a modified example of a frontinsulator, wherein FIG. 22A is a front view thereof, and FIG. 22B is across sectional view taken along the G-G line in FIG. 22A.

FIG. 23 shows explanatory diagrams of a modified example of a rearinsulator, wherein FIG. 23A is a front view thereof, and FIG. 23B is across sectional view taken along the H-H line in FIG. 23A.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is an overall view of a driver-drill 1, which serves onerepresentative, non-limiting example of a power tool according to thepresent teachings. FIG. 2 is a longitudinal cross sectional view of arear part of a main body 2 of the driver-drill 1. The representativedriver-drill 1 has an overall T shape in that a handle 3 extends in adownward (substantially perpendicular) direction from the main body 2,which extends in a rear-front direction. Furthermore, a battery pack 5constitutes a power supply for the driver-drill 1 and is mounted on amounting part 4, which is formed at a lower end of the handle 3.

A housing of the main body 2 is formed by assembling (mounting) a fronthousing 7, which houses (surrounds or encloses, at least substantially)a clutch mechanism and a spindle, onto the front (i.e., the right sidein FIG. 1) of a tubular main body housing 6, which houses a brushlessmotor 17 and a planetary gear speed reducing mechanism 72 that arediscussed below, via screws 8 screwed in from the front. Then, a caphousing 9 is assembled (mounted) on the rear of the main body housing 6via screws 10 at two locations (upper and lower), that are screwed infrom the rear. The coupling surfaces between the main body housing 6 andthe cap housing 9 form a socket and spigot joint. That is, annularprotruding parts 6 c, each of which is formed in a rear surface of themain body housing 6 and includes a screw boss into which thecorresponding screw 10 is screwed, are mated against recessed parts 9 a,which are formed in a front surface of the cap housing 9. A modechanging ring (or action mode changing ring) 11 and a clutch adjustingring 12 are provided forward of the front housing 7, and a chuck 13,which is mounted on the spindle, is provided forward of the clutchadjusting ring 12. Furthermore, the handle 3 is continuous with the mainbody housing 6, and these are formed by assembling (attaching) left andright half housings 6 a, 6 b via screws 14. Reference number 15 is atrigger that is provided on a switch housed in the handle 3. Referencenumber 16 is a motor forward/reverse changing button (reversing switchlever). A (not shown) light preferably provides illumination forward ofthe chuck 13 and is preferably disposed above the trigger 15.

The brushless motor 17 is housed in a rear part of the main body housing6 and is an inner rotor type motor that comprises a stator 18 and arotor 19 rotatably disposed within the stator 18. As shown in FIGS. 3-5,the stator 18 comprises a tubular stator core 20, which is formed from aplurality of laminated steel sheets, a front insulator 21 and a rearinsulator 22, which are respectively provided on the front and rear endsurfaces of the stator core 20 in the axial direction, and six coils 23,which are wound on the stator core 20 and through (around) the front andrear insulators 21, 22. Furthermore, a sensor circuit board 24 and ashort circuiting element 25 are attached to the front insulator 21.

The stator core 20 comprises six teeth 26 that protrude toward the axialcenter side (radially inward). Six slots 27 are respectively definedbetween adjacent pairs of the teeth 26 in the circumferential directionof the stator core 20.

The front insulator 21 is an annular, integrally-molded article(structure) and has an outer diameter that is the same (or substantiallythe same) as the outer diameter of the stator core 20. Six protrudingparts (e.g. hooks) 28 protrude in series toward the axial center side(radially inward) and are located forward of the teeth 26 of the statorcore 20. The six protruding parts 28 are formed on an innercircumferential side of the front insulator 21. In addition, six matingparts 29 respectively mate with the slots 27 of the stator core 20 andproject from a rear surface side of the front insulator 21. Six sets ofretaining parts 30 for fusing terminals (connecting terminals) 42, whichare discussed below, project from the front surface side of the frontinsulator 21 at positions that respectively correspond with the matingparts 29. In each of the retaining parts 30, a pair of projections 31,each projection 31 having a groove 32, is disposed at prescribedspacings such that the grooves 32 oppose one another. Screw bosses 33,each of which has a screw hole at its center and extends from a flangepart 34 at its base, respectively project between adjacent pairs of theretaining parts 30.

Furthermore, as is shown in FIGS. 3-5 and 7, a pair of recessed parts 35is formed on both the left and right side parts of the front insulator21 and serve as positioning parts (discussed further below). A pair oftriangular first notched parts 36, 36 is formed on the front insulator21 and also serve as positioning parts (discussed further below). Onefirst notched part 36 is defined on the upper side and one first notchedpart 36 is defined on the lower side of the corresponding recessed parts35, such that the pair of first notched parts 36 sandwich (surround orare formed in the circumferential direction outwardly of) thecorresponding recessed parts 35. Furthermore, a quadrangular secondnotched part 37 is formed at the center of an upper part of the frontinsulator 21 and also serves as a positioning part (discussed furtherbelow). The recessed parts 35, the first notched parts 36, and thesecond notched part 37 are configured or shaped such that their rearsurfaces are closed off by the stator core 20 (see e.g., FIG. 7B).

The rear insulator 22 is also annular and has the same (or substantiallythe same) outer diameter as that of the stator core 20. Six protrudingparts (e.g. hooks) 38 protrude in series toward the axial center side(radially inward) and are located rearward of the teeth 26 of the statorcore 20. The six protruding parts 38 are formed on an innercircumferential side of the rear insulator 22. In addition, six matingparts 39 mate with the slots 27 of the stator core 20 and project from afront surface side of the rear insulator 22. Furthermore, curvedtransverse notched parts 40, 40 are formed on the left and right sideparts of the rear insulator 22, and chamfer parts 41, 41, which arenotched in a straight line, are formed at the centers of the upper andlower parts of the rear insulator 22.

Furthermore, the fusing terminals (connecting terminals) 42 arerespectively retained by the retaining parts 30 of the front insulator21. Each of the fusing terminals 42 is configured (formed) by foldingover a strip-shaped metal fitting approximately in half. Each of thefusing terminals 42 comprises a first edge part 43, an intermediateregion having a portion that is bent into the shape of a protrusion, anda second edge part 44. Both side edges of the second edge part 44 arebent to form wing pieces 45, 45 that are L-shaped in a cross section.Thus, when the folded side of each of the fusing terminals 42 isinserted into its corresponding retaining part 30, and the wing pieces45 are mated with the groove parts 32 of the corresponding projections31, the fusing terminals 42 are concentric (i.e. are disposed along avirtual circle and thus are all equally spaced from a common centerpoint). Furthermore, the fusing terminals 42 are retained such that therespective first edge parts 43 face toward the outer side (radiallyoutward) with an attitude (a longitudinal orientation) that is parallelto the axial direction of the front insulator 21.

The fusing terminal 42 of the present disclosure may also be called a“thermal crimping terminal” or a “thermal caulking terminal” andgenerally enables the formation of a secure, robust connection to a leadwire (e.g., winding wire 23 a) by applying heat and pressure thereto.For example, a method of forming the electrical connection may involve,e.g., applying a sufficiently-large current to the lead wire to heat andthereby delaminate/melt the insulating coating surrounding the metalwire while the lead wire is sandwiched or interposed within the fusingterminal, and applying a crimping pressure to the fusing terminal 42 tothereby thermally crimp or clamp the lead wire to the fusing terminal42. The metal of the lead wire may thereby become fused and/or welded tothe fusing terminal 42.

In the present embodiment, the coils 23 are respectively wound aroundthe teeth 26 of the stator core 20 and through (around) the respectiveprotruding parts 28, 38 of the front and rear insulators 21, 22. In thisrespect, it is noted that just one winding wire (i.e. a singlecontinuous wire) is wound sequentially onto the respective teeth 26 thatare adjacent in the circumferential direction. All the fusing terminals42 are electrically connected to the respective winding wires 23 a bybeing fused (crimped or deformed radially inwardly) such that thewinding wires 23 a (i.e. portions of the single continuous winding wirethat respectively provide electrical connections betweencircumferentially-adjacent pairs of the coils 23) loop around the outersides of the retaining parts 30 and are respectively sandwiched (crimpedor clamped) in the fusing terminals 42, as can be best seen in FIG. 3.

Referring now to FIG. 2, the sensor circuit board 24 is equipped withthree rotation detection devices (not shown), which detect the positionsof permanent magnets 63 provided on the rotor 19 and output rotationdetection signals. As can be seen in FIG. 5, the sensor circuit board 24has an overall doughnut shape and its outer diameter fits within theradially inner sides of the retaining parts 30. Furthermore, as is alsoshown in FIG. 6, four projections 46 have through holes 47 thatcorrespond to the screw bosses 33 of the front insulator 21 and extendat the outer circumference of the sensor circuit board 24. Due to thefact that the screw bosses 33 respectively pass through the throughholes 47, the projections 46 respectively make contact with the flangeparts 34 and are positioned at the front surface of the front insulator21. A leader part 48 for signal lines 49 of the rotation detectiondevices is provided at the center of a lower part of the sensor circuitboard 24, and a heat shrink tube 48 a, which includes an adhesive,covers and extends across the leader part 48 and the signal lines 49.Using the heat shrink tube 48 a makes it possible to simultaneouslywaterproof and prevent a break in the signal lines 49.

Further explanation of the representative short circuiting element 25will now be provided with reference to FIGS. 8 and 9. As shown therein,four tubular bosses 51 are configured to respectively mate with thescrew bosses 33 of the front insulator 21 from the rear. The fourtubular bosses 51 integrally project at the outer circumference of anannular, resin insulation part 50, whose outer diameter is substantiallythe same as the outer diameter of the sensor circuit board 24. Inaddition, as can also be seen in FIG. 10, three sheet metal elements,namely, a first sheet metal element 52A, a second sheet metal element52B, and a third sheet metal element 52C, are insert molded in theinsulation part 50. The first sheet metal element 52A is formed byradially outwardly bending a pair of short circuiting pieces (tabs orterminals) 53, 53, which are respectively extend from the left and rightends of a (lower) coupling part 54A. The coupling part 54A is curved ina U shape and is longitudinally oriented such that its thicknessdirection is in the radial direction of the stator 18. The second sheetmetal element 52B comprises a pair of short circuiting pieces (tabs orterminals) 53, 53 on the lower right and the upper left of a couplingpart 54B, which is on the left side, is arcuately curved, and islongitudinally oriented such that its thickness direction is therear-front direction of the stator 18. A center portion of the couplingpart 54B is offset rearward by bent parts 54 d, 54 d. The third sheetmetal element 52C comprises a pair of short circuiting pieces (tabs orterminals) 53, 53 respectively extending from the lower left and theupper right of a coupling part 54C, which is on the right side and isarcuately curved. A transversely-oriented semicircular portion of thecoupling part 54C is offset rearward from the short circuiting piece 53on the lower left of the coupling part 54C by a bent part 54 d. Theremaining semicircular portion is curved on the inner side in alongitudinal orientation via a folded part 54 e. The short circuitingpiece 53 on the upper right is bent outward. The sheet metal elements52A-52C each have a semi-circular shape in radial cross-section. Asshown in FIG. 11, these three sheet metal elements 52A-52C are insertmolded (embedded) in the insulation part 50 in a state wherein thesecond sheet metal element 52B is disposed rearward of and on the leftside of the first sheet metal element 52A, the third sheet metal element52C is disposed rearward of and on the right side of the first sheetmetal element 52A, and such that the sheet metal elements 52A-52Cconcentrically overlap without contacting each other. Therefore, theinsulation part 50 retains or holds the sheet metal elements 52A-52C ina physically and electrically separated state, i.e. they areelectronically isolated from each other.

Therefore, at the outer circumference of the insulation part 50, therespective pairs of short circuiting pieces 53 (six in total), which aredisposed diagonally (diametrically) opposite one another and areelectrically interconnected, radially project in correspondence with thefusing terminals 42 retained by the front insulator 21. Slits (slots)55, into which the second edge parts 44 of the fusing terminals 42 canbe respectively inserted, are formed at or in the tips (radially outerportions) of the short circuiting pieces 53.

Furthermore, referring to FIG. 11, a connecting piece 56 is locatedbetween the short circuiting piece 53 on the lower side of the secondsheet metal element 52B and the short circuiting piece 53 on the lowerside of the third sheet metal element 52C. The connecting piece 56 isformed downward facing at the center of a lower end of the coupling part54A of the first sheet metal element 52A. The U-phase, V-phase, andW-phase power supply lines 57 are respectively spot welded to the rearsurface of the short circuiting piece 53 on the lower side of the secondsheet metal element 52B, the short circuiting piece 53 on the lower sideof the third sheet metal element 52C, and the connecting piece 56. Asshown in FIGS. 10 and 11, two projections 56 a, 56 a increase thecoupling strength to the insulation part 50 and are formed on the leftand right of the connecting piece 56. Guide ribs 58 partition therespective power supply lines 57, guide the power supply lines 57downward from the sheet metal elements 52A-52C, retain the power supplylines 57, and are disposed in the up-down direction. The guide ribs 58are provided in parallel, integrally, and erectly to a lower end backsurface of the insulation part 50. In addition, as shown in the rearsurface view of the insulation part 50 in FIG. 9C, guide projections 50a respectively guide the left and right power supply lines 57 to theshort circuiting pieces 53 side, and are formed on an upper side of theguide ribs 58. Recessed parts 50 b, 50 b for positioning are formed onan inner circumferential side of the insulation part 50. As shown inFIG. 10, a through hole 50 c for exposing the connecting piece 56 andthereby increasing its heat dissipating capacity is formed in a lowerpart of the insulation part 50. Positions P shown in FIGS. 8, 10 are thelocations at which the respective power supply lines 57 are welded.

In the assembled state, the short circuiting element 25 overlaps thesensor circuit board 24 from the front such that the screw bosses 33 ofthe front insulator 21 are inserted into the bosses 51 and the shortcircuiting element 25 is affixed thereto by screws 88. Furthermore, thesecond edge parts 44 of the fusing terminals 42 are respectivelyinserted into the slits 55 of the corresponding short circuiting pieces53. In the present embodiment, the sheet metal elements 52A-52C are notexposed at the rear surface of the insulation part 50 and therefore donot contact the sensor circuit board 24 due to the intervening resin ofthe insulating part 50. Furthermore, the center hole of the sensorcircuit board 24 is preferably smaller than the center hole of the shortcircuiting element 25 in the present embodiment.

If the fusing terminals 42 and the short circuiting pieces 53 aresoldered in this state, then the respective pairs of fusing terminals42, 42, which are located with point symmetry (i.e. diametricallyopposite of each other), are short circuited (shunted or electricallyconnected) by the first through third sheet metal elements 52A-52C.Thus, as shown in the wiring diagram of FIG. 12, each of the fusingterminals 42 is electrically connected to one of the winding wires 23 abetween circumferentially-adjacent coils sequentially wound around thestator core 20. Further, respective pairs of fusing terminals 42 thatare diagonally (diametrically) opposite one another are electricallyinterconnected by the first through third sheet metal elements 52A-52C,thereby forming a parallel-winding delta connection. Reference symbol Sis the start of the winding (i.e. the single continuous winding wire),and reference symbol E is the end of the same winding.

In the present embodiment, because the fusing terminals 42 and the shortcircuiting element 25 are separate bodies, and the short circuitingpieces 53 of the short circuiting element 25 are soldered onto thefusing terminals 42 after the coils 23 have been wound, the shortcircuiting element 25 is not a hindrance during the manufacturing stepof winding the respective coils 23 on the teeth 26 of the stator core 20and on the front and rear insulators 21, 22.

In addition, the fusing terminals 42 are formed with a sufficient height(axial length) to provide a stable and durable connection (joining).However, as shown in e.g., FIG. 2, FIG. 7(B), the sensor circuit board24 and the short circuiting element 25 fit within the height (axiallength) dimension of the fusing terminals 42, and consequently theentire (axial) length of the brushless motor 17 is kept to a minimumeven though the short circuiting element 25, etc. are used (installed).Furthermore, except for the signal lines, the power supply lines, andthe like, all the elements fit within the outer diameter of the statorcore 20. Consequently, the outer diameter of the product also does notincrease, and the product is therefore compact.

As shown in FIG. 13, the thus-assembled stator 18 is housed (supported)while being positioned in the axial direction and in the circumferentialdirection in the following manner. The outer circumference of the statorcore 20 is held by support ribs 59, which project in the circumferentialdirections from the inner surfaces of the half housings 6 a, 6 b of themain body housing 6. In addition, the outer circumference of the statorcore 20 is also held by projections 60, which project from the innersurface of the half housing 6 a and respectively mate with the recessedparts 35, which are formed (defined) in the side surface of the frontinsulator 21. Furthermore, when the stator 18 is to be housed in thehalf housings 6 a, 6 b, the assembly is done while ensuring that theplanar surfaces of the chamfer parts 41 do not contact the support ribs59, which makes it easy to perform the assembly in the desiredorientation. The recessed part at the center of each of the projections60 has a reduced thickness; therefore, if the projections 60 are formedalso in the half housing 6 b, the stator 18 can be more suitably held.

Moreover, as shown in FIG. 2, the rotor 19 comprises: a rotary shaft 61,which is located at the axial center; a tubular rotor core 62, which isdisposed around the rotary shaft 61; and the permanent magnets 63, whichare disposed on the outer side of the rotor core 62 and have polaritiesthat alternate in the circumferential direction of the cylindricalshape.

The rear end of the rotary shaft 61 is pivotally supported by a bearing64, which is held by the cap housing 9, and a centrifugal fan 65 isattached at a forward position thereof. In the present embodiment, acenter part of the centrifugal fan 65 bulges forward so as to form acone shape, and the bearing 64 has a shape that projects rearwardtherefrom. Due to this design, the distance between the cap housing 9and the centrifugal fan 65 becomes shorter (can be decreased), resultingin a shortening of the overall length of the driver-drill 1. Referencenumbers 66 are air suction ports (FIG. 1) that are respectively formedon the left and right side surfaces of the main body housing 6, andreference numbers 67 are exhaust ports (FIGS. 1, 2) that arerespectively formed on the left and right side surfaces of the caphousing 9.

In addition, as shown in FIG. 2, a gear case 68 houses (surrounds) theplanetary gear speed reducing mechanism 72 and is provided forward ofthe brushless motor 17. The front end of the rotary shaft 61 is insertedthrough a cap 69, which closes up a rear end of the gear case 68, and ispivotally supported by a bearing 70, which is held by the cap 69. Apinion 71 is fastened to the front end of the rotary shaft 61.

The planetary gear speed reducing mechanism 72 has a well-knownstructure. A plurality of carriers 75 respectively support a pluralityof planetary gears 74, 74 that revolve inside an internal gear 73, andare provided in parallel in the axial direction. Furthermore, a secondstage internal gear (denoted as reference number 73A in order todistinguish such) is provided such that it can move frontward andrearward in the axial directions between an advanced position and aretracted position. In the advanced position, the second stage internalgear is fixed inside the gear case 68 and the second stage planetarygears 74 are caused to revolve. In the retracted position, the secondstage planetary gears 74 and the first stage carriers 75 aresimultaneously engaged, the carriers 75 and the planetary gears 74 arecaused to rotate integrally, and the second stage speed reduction iscanceled. A speed changing ring 77 is coupled to the internal gear 73Avia pins 76. A projection 78 at an upper end of the speed changing ring77 is coupled to a speed changing button (speed changing lever) 80 viafront and rear coil springs 79, 79. By sliding the speed changing button80 to the front or to the rear, the internal gear 73A is caused torespectively move frontward and rearward via the speed changing ring 77,making it possible to select a low speed mode at the advanced positionand a high speed mode at the retracted position.

In the driver-drill 1 configured as described above, when the trigger 15is squeezed, the switch turns ON and the brushless motor 17 is driven bythe power supply of the battery pack 5. That is, a not-shownmicrocontroller of a controller, which is housed in the lower part ofthe handle 3, determines the rotational state of the rotor 19 byobtaining the rotation detection signals, which indicate the positionsof the permanent magnets 63 of the rotor 19, output from the rotationdetection devices of the sensor circuit board 24, and controls theON/OFF state of each of the switching devices in accordance with thedetermined rotational state. Then, the rotor 19 is rotated bysequentially supplying electric current to each of the(diametrically-opposite pairs of) coils 23 of the stator 18. This causesthe rotary shaft 61 to rotate, and the rotation, the speed of which isreduced by the planetary gear speed reducing mechanism 72, istransmitted to the spindle and rotates the chuck 13. By rotating themode changing ring 11, it is possible to select either the driving mode,wherein the transmission of rotation at the prescribed torque is blockedand the clutch mechanism functions, or a drilling mode, wherein theclutch mechanism does not function. Furthermore, by operating the clutchadjusting ring 12, the torque, at which the clutch mechanism operates inthe driving mode, can be adjusted.

Furthermore, because the coils 23 of the present brushless motor 17 arein the parallelly wound state, the electrical resistance of the windingis reduced and a large current can be supplied. This parallelly woundstate can be achieved by using the short circuiting element 25, whichmakes it possible to save space. That is, as shown in FIG. 2, becausethe relatively-thin short circuiting element 25 is disposed within theinner sides of the retaining parts 30 and is assembled such that theshort circuiting element 25 does not protrude forward of the tips of theprojections 31 of the retaining parts 30, the space forward of thesensor circuit board 24 can be used effectively (efficiently) to installthe short circuiting element 25, thereby making the compact sizemaintainable.

In addition, because the six coils 23 are wound with a single windingwire (i.e. a single wire having no breaks or interruptions in it), allthe coils 23 can be completely wound in a single manufacturing step, andcrossover wires for connecting coils wound around the teeth that arediametrically positioned (opposed) become unnecessary. The absence ofcrossover wires also leads to making the product compact.

Furthermore, because the sensor circuit board 24 is provided on one endside of the brushless motor 17 and the power is supplied to the coils 23from the same side, it becomes possible to supply a large current whilemaintaining the compact size. In particular, because the sensor circuitboard 24 and the short circuiting element 25 are arranged in order(successively) on the one end side of the stator 18, the sensitivity ofthe sensors is satisfactory.

Furthermore, in the above-mentioned embodiment, a structure is utilizedin which the brushless motor 17 is housed in the main body housing 6,which is formed of the two half housings 6 a, 6 b. However, as shown in,for example, FIGS. 14-16, if the brushless motor 17 is housed in atubular housing that is used in a circular saw or the like, then, in thestate wherein the stator 18 of the brushless motor 17 is orientedrearward, the short circuiting element 25 side being rearward, a bottompart of a tubular housing 81 is provided with four L-shaped receivingribs 82, whose tips mate with the four first notched parts 36 of thefront insulator 21 of the stator 18 and which make contact with the endsurface of the stator core 20. A plate-shaped rotation stopping rib 83has a tip that mates with the second notched part 37 of the frontinsulator 21 and it makes contact with the end surface of the statorcore 20. Furthermore, in front of these, pairs of longitudinal ribs 84make contact with a circumferential surface of the stator 18 and areprovided with up-down and left-right symmetry. Reference number 81 a isa housing recessed part of a bearing. Thus, providing the tubularhousing 81 with engagement portions between the insulator and the statormakes it possible to suitably assemble the stator 18.

In addition, screw bosses 85 are provided with heights are such that thescrew bosses 85, 85 are flush with the end surface of the stator core 20in the housed state. The screw bosses 85 are respectively providedbetween the left longitudinal ribs 84, 84 and between the rightlongitudinal ribs 84, 84. Furthermore, by tightening the screws 86 fromthe front through the washers 87 into the screw bosses 85, it ispossible to mate the washers 87 against the transverse notched parts 40of the rear insulator 22 and thereby to press the end surface of thestator core 20 from the front.

As a result of this design, the stator 18 is prevented from movingrearward by the receiving ribs 82 and is prevented from moving in thecircumferential direction by the rotation stopping rib 83. Moreover, thestator 18 is centered inside the tubular housing 81 by the longitudinalribs 84. Furthermore, forward movement is prevented by the screws 86 andthe washers 87. In addition, because a guide part 21 a projects from thefront insulator 21, when the stator 18 is pressed in, the stator 18 canbe smoothly set to the target position if the guide part 21 a is pressedin such that it fits between the longitudinal ribs 84, 84, as shown inFIG. 15A. After being pressed in, it is also positioned in thecircumferential direction.

Thus, in embodiments having a tubular housing 81 as well, the stator 18can be positioned simply by using the notched parts 36, 37, 40 providedin the front and rear insulators 21, 22, and it also becomes possible tostandardize the front and rear insulators 21, 22.

Moreover, although in the above-mentioned embodiment the signal lines 49of the sensor circuit board 24 extend from the same side (i.e., thelower side) as the power supply lines 57 of the short circuiting element25 (see FIG. 7B), the signal lines 49 may extend from the upper side bychanging (rotating) the phase (orientation) of the sensor circuit board24 by 180°, which embodiment is exemplified by the stator 18 shown inFIG. 17 (compare the orientation of the sensor circuit boards in FIGS. 3and 17). Thus, as in, for example, a grinder 90 as shown in FIG. 18,even if a (tubular) motor housing 91 that houses the brushless motor 17also serves as a grip part, the motor housing 91 is prevented fromprotruding on the power supply lines 57 side, and thereby the motorhousing 91 can be narrowed at that portion. In addition, in terms ofother aspects of the structure as well, the wiring is simpler and,moreover, the insulator can also be standardized. Furthermore, in FIG.18: reference number 92 is a controller; reference number 93 is a switchthat is connected to the controller 92 via a lead wire 94; referencenumber 95 is a slide button that turns the switch 93 ON and OFF via alinking bar 96; and reference number 97 is a front housing having adownwardly-protruding spindle 98.

Furthermore, the sensor circuit board 24 can also be provided on theside of the stator core 20 opposite the short circuiting element 25.That is, in an alternative embodiment of a stator 18A as shown in FIGS.19-21, the sensor circuit board 24 is provided on the rear surface ofthe rear insulator 22, and therefore transverse notched parts 22 a and achamfer part 22 b are formed, in accordance with the transverse notchedparts 40 and the chamfer part 41 provided on the rear insulator 22, onthe outer circumference of the sensor circuit board 24, which makes itpossible to also assemble the stator 18A in a tubular housing. Referencenumbers 99 are screws, and reference numbers 100 are rotation detectiondevices (Hall-effect ICs). In this embodiment, the positions ofpermanent magnets provided on the centrifugal fan 65 are detected by therotation detection devices 100. In the present design, the shortcircuiting element 25 is assembled in the front insulator 21 withouttransiting the sensor circuit board 24. However, because the shortcircuiting element 25 mates and seats the recessed parts on the rearsurface sides of the bosses 51 to and in the upper surfaces of the screwbosses 33 of the front insulator 21, the position of the shortcircuiting element 25 does not change even without the sensor circuitboard 24. The short circuiting element 25 is positioned by the mating ofthe recesses and protrusions between the screw bosses 33 and the bosses51. In FIG. 19, a plurality of projections 22 c integrally project fromthe rear surface of the rear insulator 22, and the sensor circuit board24 is retained by inserting the projections in through holes provided inthe sensor circuit board 24 and then thermally deforming theprojections.

Moreover, the structures of the insulators also can be modified ifnecessary. FIGS. 22A and B show a modified example of the frontinsulator 21, and FIGS. 23A and B show a modified example of the rearinsulator 22. As shown in FIGS. 22A and B, recessed grooves 28 a areformed in the front insulator 21, in directions orthogonal to theprotruding parts 28, on the front surface sides of the bases of theprotruding parts 28. In addition, relief parts 28 b, 28 b, which arerecessed in the radial directions, are formed on both sides in thecircumferential direction of the bases of the protruding parts 28.Likewise, as shown in FIGS. 23A and B, recessed grooves 38 a are alsoformed in the rear insulator 22, in directions orthogonal to theprotruding parts 38, on the rear surface sides of the bases of theprotruding parts 38. In addition, relief parts 38 b, 38 b, which arerecessed in the radial directions, are formed on both sides in thecircumferential direction of the bases of the protruding parts 38.

Each one of the winding wires of the coils 23 in the teeth 26 starts itswinding by being fitted in the recessed grooves 28 a, 38 a, such thatthe coil of the first winding is held exactly at the base of one of theteeth, and the coils of the second and subsequent windings aresuccessively wound in series around the respective bases of thecircumferentially adjacent teeth.

In addition, a nozzle for winding the coils 23 easily passes through therelief parts 28 b, 38 b. Furthermore, hollow parts 38 c for smoothlywinding the coils 23 are also formed on both sides of the bases of theprotruding parts 38 on the inner circumferential surface of the rearinsulator 22.

Furthermore, because the transverse notched parts 40, 40 are locatedbetween protruding parts 38, 38, and because protruding parts 38 arelocated in the portions of the widths across the respective flats of thechamfer parts 41, 41, the outer circumference of the rear insulator 22is not enlarged.

Furthermore, in the above-described embodiments, the short circuitingmeans comprises the short circuiting element(s) and the fusingterminals; however, it is also possible, for example: to omit the fusingterminals and to short circuit (electrically connect or shunt) thewinding wires with just the short circuiting element(s); conversely, itis also possible to omit the short circuiting element(s) and tointerconnect the fusing terminals with lead wires, etc.

In addition, the power tool is not limited to a type that drives a toolaccessory, such as a driver-drill, a circular saw, or a grinder, and thepresent invention can also be adapted, for example and withoutlimitation, to vacuum cleaners and, furthermore, to gardening tools suchas a blower. In addition, the present invention can also be adapted topower tools that use a sensor-less brushless motor and therefore have nosensor circuit board.

As used herein, the term “short circuit” is generally intended to mean alow resistance electrical connection such as a metal plate material ormetal wire material. Preferably, no additional resistive element (e.g.,a ceramic resistor) is added to the short circuit electrical path, butit is sufficient if the short circuit acts, e.g., as a shunt, i.e. oneor more small or low resistance elements may be added to the shortcircuit electrical path, if appropriate for the particular design.Although metal sheet (plate) elements were used in the above-describedrepresentative embodiments, the short circuit electrical connections mayalso be in the form of a wire (i.e. round or oval shapes) as long as thewire has a sufficient diameter (thickness) to handle the rated currentthat is expected to flow through it.

REFERENCE NUMBER LIST

-   1 Driver-drill-   2 Main body-   6 Main body housing-   6 a, 6 b Housing halves-   17 Brushless motor-   18 Stator-   19 Rotor-   20 Stator core-   21 Front insulator-   22 Rear insulator-   23 Coil-   23 a Winding wire-   24 Sensor circuit board-   25 Short circuiting element-   28 Protruding part-   30 Retaining part-   31 Projection-   35 Recessed part-   36 First notched part-   37 Second notched part-   38 Protruding part-   40 Transverse notched part-   42 Fusing terminal-   43 First edge part of fusing terminal 42-   44 Second edge part of fusing terminal 42-   49 Signal line-   50 Insulation part-   52A First sheet metal element-   52B Second sheet metal element-   52C Third sheet metal element-   53 Short circuiting piece-   54 Coupling part-   57 Power supply line-   61 Rotary shaft-   63 Permanent magnet-   81 Tubular housing-   82 Receiving rib-   83 Rotation stopping rib-   84 Longitudinal rib-   90 Grinder-   91 Motor housing-   100 Rotation detection devices (Hall-effect ICs)

We claim:
 1. A power tool comprising: a motor having a stator and arotor, the stator including front and rear insulators respectivelydisposed forward and rearward of a stator core in an axial directionthereof, at least six coils respectively wound on the stator such thatthe coils are wound through the front and rear insulators, winding wiresrespectively electrically connecting circumferentially-adjacent pairs ofthe coils and a short circuiting means that short circuits respectivepairs of the winding wires that are positioned diagonally across fromone another.
 2. The power tool according to claim 1, wherein all of thecoils are wound with a single continuous winding wire.
 3. The power toolaccording to claim 1, wherein the short circuiting means comprises: aplurality of sheet metal elements that respectively electricallyinterconnect the pairs of winding wires that are positioned diagonallyacross from one another, and an insulation part, which is made of resinand retains the sheet metal elements.
 4. The power tool according toclaim 3, wherein the sheet metal elements each have a semi-circularshape in a radial direction of the short circuiting means and areembedded in the resin of the insulating part so to be electricallyisolated from each other.
 5. The power tool according to claim 4,wherein the sheet metal elements each have two short circuiting piecesthat are disposed radially opposite of each other and are respectivelyaligned with diagonally-opposite winding wires.
 6. The power toolaccording to claim 5, wherein the short circuiting means has three sheetmetal elements that are respectively electrically connected to U-phase,V-phase, and W-phase power supply lines.
 7. The power tool according toclaim 6, wherein all of the coils are wound with a single continuouswinding wire.
 8. The power tool according to claim 1, wherein the shortcircuiting means comprises lead wires that respectively electricallyinterconnect the pairs of winding wires that are positioned diagonallyacross from one another.
 9. The power tool according to claim 1, furthercomprising: a sensor circuit board provided between the short circuitingmeans and one of the front or rear insulator, the sensor circuit boardhaving at least one rotation detection device for detecting positions ofpermanent magnets provided on the rotor or on a centrifugal fan.
 10. Thepower tool according to claim 9, wherein the sensor circuit board isconfigured to be mounted in more than one rotational orientation. 11.The power tool according to claim 1, wherein: the short circuiting meansis annular and has an outer diameter that is at least substantially thesame as the outer diameter of the stator core, the front insulator isannular and has an outer diameter that is at least substantially thesame as the outer diameter of the stator core, the rear insulator isannular and has an outer diameter that is at least substantially thesame as the outer diameter of the stator core, and protruding partsradially-inwardly project from an inner circumferential surface of eachof the front and rear insulators in series in the circumferentialdirection, the coils being respectively wrapped around correspondingprotruding parts.
 12. The power tool according to claim 1, wherein: oneof the front and the rear insulator retains a plurality of fusingterminals that are circumferentially-arranged along an outer diameterthereof, and the fusing terminals respectively connect the winding wiresto the short circuiting means.
 13. The power tool according to claim 12,wherein: the fusing terminals each comprise a folded-over metal stripand the winding wires are respectively sandwiched between first andsecond edges of the fusing terminals.
 14. The power tool according toclaim 13, wherein the fusing terminals are respectively electricallyconnected to corresponding short circuiting pieces of the shortcircuiting means, the short circuiting pieces each extending in a radialdirection of the stator core.
 15. The power tool according to claim 14,wherein: the short circuiting means is annular and has an outer diameterthat is at least substantially the same as the outer diameter of thestator core, the front insulator is annular and has an outer diameterthat is at least substantially the same as the outer diameter of thestator core, the rear insulator is annular and has an outer diameterthat is at least substantially the same as the outer diameter of thestator core, and protruding parts radially-inwardly project from aninner circumferential surface of each of the front and rear insulatorsin series in the circumferential direction, the coils being respectivelywrapped around corresponding protruding parts.
 16. The power toolaccording to claim 15, further comprising: a sensor circuit boardprovided between the short circuiting means and one of the front or rearinsulator, the sensor circuit board having at least one rotationdetection device for detecting positions of permanent magnets providedon the rotor or on a centrifugal fan.
 17. The power tool according toclaim 16, wherein the short circuiting means comprises: a plurality ofsheet metal elements that respectively electrically interconnect thepairs of winding wires that are positioned diagonally across from oneanother, and an insulation part, which is made of resin and retains thesheet metal elements, wherein the sheet metal elements each have asemi-circular shape in a radial direction of the short circuiting meansand are embedded in the resin of the insulating part so to beelectrically isolated from each other and the sheet metal elements eachhave two short circuiting pieces that are disposed radially opposite ofeach other and are respectively aligned with diagonally-opposite windingwires.
 18. The power tool according to claim 17, wherein: the shortcircuiting means has three sheet metal elements that are respectivelyelectrically connected to U-phase, V-phase, and W-phase power supplylines, and all of the coils are wound with a single continuous windingwire.
 19. A power tool comprising: a motor having a stator and a rotor,the stator including front and rear insulators respectively disposedforward and rearward of a stator core in an axial direction thereof, aplurality of coils respectively wound on the stator such that the coilsare wound through the front and rear insulators, and a housing thathouses the motor and is formed by combining a pair of half housings,wherein the stator includes positioning parts that engage withrespective inner surfaces of the half housings, the positioning partspreferably being provided on one of the first and second insulator. 20.A power tool comprising: a motor having a stator and a rotor, the statorincluding front and rear insulators respectively disposed forward andrearward of a stator core in an axial direction thereof, a plurality ofcoils respectively wound on the stator such that the coils are woundthrough the front and rear insulators and an integral tubular housingthat houses the motor, wherein the stator is provided with at least onepositioning part that engages with an inner surface of the tubularhousing, the at least one positioning part preferably being provided onone of the first and second insulator.